The present invention relates generally to braking systems and, more specifically, to brake actuators. Even more particularly, the present invention relates to a tamper-resistant riveted spring brake actuator and a method of assembling the same.
Fluid-operated braking systems have long been used to control the movement of motor vehicles in a safe and effective manner. In particular, air brakes are commonly used on commercial vehicles such as trucks, which typically have large gross vehicle weights. The considerable inertial mass of these heavy-duty vehicles in combination with the high speeds at which they travel requires a braking system which responds rapidly with substantial braking power. One system component which is instrumental in the operation of air brake systems is the brake actuator, which provides the force necessary when braking a vehicle.
In a typical double diaphragm spring brake actuator, a barrel-shaped power spring stores potential energy and exerts the large force required for braking in case of air pressure failure. Air pressure acting on a diaphragm compresses the power spring and maintains it in its brake release position. When the air is exhausted, the power spring acts on the diaphragm, typically an elastomeric diaphragm or a piston, and thereby applies the brakes in case of failure of the system air pressure.
The power spring is positioned in a spring chamber, which is typically formed by clamping an elastomeric diaphragm between a head (sometimes also known as a spring housing or spring chamber) and a flange case (sometimes known as an adaptor). The power spring is compressed within the spring chamber between the head and the diaphragm. The power spring has a high spring constant and is normally compressed to a height of less than 3 inches from an original uncompressed height of from 9 to 12 inches. The power spring, therefore, stores a substantial amount of potential energy, usually exerting a force on the head of about 2,000 to 3,000 pounds.
Unauthorized removal of the head, therefore, could be dangerous due to the large potential energy of the power spring. In addition, unauthorized replacement of the head could result in a poor diaphragm seal or other internal defects. Therefore, it is conventional to discourage unauthorized removal and replacement of the head by attaching a warning label and/or providing a securing means which is tamper-resistant or at least tamper-evident, such that a new securing means, not readily available to unauthorized personnel is required before the head can be reattached.
Various approaches have been heretofore proposed for securing the brake actuator head to the flange case to prevent improvident disassembly of the two parts. GB Patent No. 2,000,225, for example, discloses in one embodiment a brake actuator including a head secured to a flange case with a circlip. The circlip is seated in an inwardly facing groove of the flange case and extends over an annular lip of the head, such that the head can only be separated from the flange case by deforming or destroying the flange case. The circlip, however, is accessible from between the flange case and an edge of the head and, therefore, could possibly be tampered with. Moreover, the design is complex, and therefore difficult and costly to manufacture and assemble.
The ""225 patent, in another embodiment, also discloses a brake actuator including a head having a lower edge that is spun, or in elastically deformed, over a flange case, such that the head can only be separated from the flange case by deforming or destroying the lower edge of the head. Similar arrangements are also disclosed in U.S. Pat. Nos. 4,850,263, 4,960,036, 5,067,391, 5,205,205, 5,263,403, 5,311,809, 5,433,138, and 5,640,894. A disadvantage of each of these prior art references is that special deforming machinery is needed to assemble the brake actuator, making assembly both costly and difficult. Another disadvantage is that the deformed lower edge of the head can easily be undeformed by an unauthorized person attempting to disassemble the brake actuator.
U.S. Pat. No. 5,285,716 discloses a brake actuator having a head and a flange case welded together in a tamper-proof manner. As disclosed in the patent, however, it is a relatively easy task to grind away the weld to remove the head. In addition, the flange case must disadvantageously be made of steel in order to be welded to the steel head. Flange cases are normally made of aluminum.
U.S. Pat. Nos. 5,315,918 and 5,353,688 both disclose, in one embodiment, a brake actuator including a head screwed onto a flange case and secured with an insert or a pin creating an interference fit. The insert or pin may be welded in place. In another embodiment of the ""918 and ""688 patents, and in U.S. Pat. No. 4,887,513, a brake actuator is disclosed having a head which is joined to a flange case with a bayonet connection. U.S. Pat. No. 5,560,280 discloses a spring chamber head and adapter head, which include a plurality of cooperating peripheral lugs and flanges thereon. The flanges are held in registration with the lugs by the compression of the periphery of the spring brake diaphragm between the heads. A disadvantage of each of these prior art references is that the design is complex, and therefore difficult and costly to manufacture and assemble. A related disadvantage is that special and complex machinery is needed to assemble the brake actuator, making assembly even more costly and difficult.
What is desired, therefore, is a spring brake actuator which is tamper resistant, which is simple in design as compared with known spring brake actuators, which is relatively easy and inexpensive to produce and assemble, which does not require special machinery to assemble, and which can be made of conventional materials.
Accordingly, it is an object of the present invention to provide a spring brake actuator which is tamper resistant.
Another object of the present invention is to provide a spring brake actuator having the above characteristics and which is simple in design as compared with known spring brake actuators.
A further object of the present invention is to provide a spring brake actuator having the above characteristics and which is relatively easy and inexpensive to produce and assemble.
Still another object of the present invention is to provide a spring brake actuator having the above characteristics and which does not require special machinery to assemble.
Yet a further object of the present invention is to provide a spring brake actuator having the above characteristics and which can be made of conventional materials.
These and other objects of the present invention are achieved by provision of a spring brake actuator having a flange case and a head. The flange case and the head each have a radially outwardly extending annular flange having a plurality of radially spaced apart axial holes passing therethrough which correspond to and align with each other. A diaphragm is clamped in a fluid tight manner between the annular flange of the head and the annular flange of the flange case. A plurality of disassembleable fastening members pass through the holes in the annular flange of the head and the holes in the annular flange of the flange case in order to undetachably secure the head on the flange case.
In one embodiment, the disassembleable fastening members are rivets, while in another embodiment, the disassembleable fastening members are disassembleable nut and bolt pairs, wherein the nuts are preferably welded to the bolts.
Preferably, the diaphragm includes a periphery which comprises an annular widened portion having a thickness greater than a thickness of the remainder of the diaphragm. When such is the case, the annular flange of the head may further comprises an annular groove adapted to receive the annular widened portion of the periphery of the diaphragm. The annular groove may be defined, for example, by bends in metal defining the flange in which the groove is formed. The annular flange of the flange case may also further comprise an annular groove adapted to receive the annular widened portion of the periphery of the diaphragm. The annular groove may be defined by two annularly extending flange portions with an axially extending flange portion extending therebetween, which together define the annular flange of the flange case.
In another aspect, the present invention relates to a method of assembling such a spring brake actuator.
The invention and its particular features and advantages will become more apparent from the following detailed description considered with reference to the accompanying drawings.